1. Field of the Invention
The present invention relates generally to structural joints and, more particularly, to a structural joint of the tapered variety which is especially effective when subjected to bending stresses.
2. Description of the Prior Art
The joining together of structural members such that the members experience minimal relative motion when subjected to loading is a classic and perplexing problem. Many methods and constructions have been explored in attempts to solve to the problem. Among them are screw threads, including the modern spiral lock type, and the locking taper.
The locking taper was initially designed to join rotating elements and is used in many applications including aerospace, automotive and general machinery. Conventional locking tapers are of three main types, namely, Morse, Brown and Sharpe, and Jarno. The major difference between these types of tapers is the angle of the mated tapered cones. It is generally considered that a set of cones is of the locking type when the included angle is less than 6 degrees. The locking taper provides limited resistance to torsion, bending, and distraction of the components it joins, and is ideally suited for rotating spindles experiencing moderate side loading.
However when bending is the predominant mode of loading, certain problems arise with the use of conventional locking tapers. Specifically when a bending moment is imparted to the system, deflection of the components causes impingement of the male member against the female member at the mouth of the female member. This impingement causes a point loading stress concentration combined with the adverse effects of relative motion and resultant wear when subjected to cyclic bending. If material is removed from the male member to accommodate this condition, the section modulus decreases and localized stresses increase to the point of failure.
One obvious solution is to flare the mouth of the female portion such that impingement of the male member against the female member never occurs at that location. Of course, this is only possible when the female member is of sufficient size to accommodate formation of a flare. This solution is also impractical insofar as it is rather difficult to manufacture.
The prior art includes numerous examples of tapered joints. Many of them relate to tubes and pipes and attempts to seal the tubes and pipes against leakage. Typical of such constructions are the U.S. Patents to Handa et al., No. 4,623,173; to Saunders et al., No. 4,549,754; to Coberly et al., No. 3,494,642; to Giovanazzi et al., No. 3,264,012; to Holycross et al., No. 2,795,440; to Frances, No. 2,331,020; and to True, No. 1,896,261.
A different mode of construction is presented in the patent to Holycross et al, No. 2,795,440. While stress relief of the joint is said to be of concern, the subject of the Holycross et al invention is tubular in its configuration and relates to a concentric chamfer to provide increased volume to receive cement used for sealing purposes.
U.S. Pat. No. 3,655,244 discloses a percussion tool which utilizes a recessed end for mating reception of a tool element. Mating surfaces of the recessed end and of the tool element are mathematically generated to assure ease of initial installation and subsequent removal of the tool element.
Unfortunately, none of the foregoing known constructions provides a solid joint which can be readily assembled and disassembled, is capable of withstanding extreme stresses in torsion, compression, and bending as well as intermittent and shock loading of the type which is imparted when the joint is used, for example, in a prosthetic manner in the human body.